1. Field of the Invention
The present disclosure relates generally to the field of hydrocarbon fluid measurements, and relates more particularly, but not by way of limitation, to a method and apparatus for measuring the flow rate of a fluid in a hydrocarbon well.
2. Brief Description of Related Art
Differential pressure measurement can allow a determination of fluid flow rate when combined with various physical properties of a fluid, such as density. Current methods for measuring pressure differences consist of utilizing either a differential pressure sensor/gauge or two absolute pressure sensors. Differential pressure gauges are extremely difficult and sometimes impossible to implement in downhole oilfield applications. Most differential pressure gauges, for accurate measurement of small differential pressures (in the range of 1 to 100 psi), require a very thin sensitive membrane (about 10-50 micron thick), have trouble withstanding large pressure surges on the order of a few hundreds, or a few thousands of psi, or acceleration during mechanical shocks. For example, severe pressure surges and extreme mechanical shocks often occur downhole in hydrocarbon wells from events such as perforating. Moreover, differential pressure gauges generally require a column of the hydraulic fluid flowing through the downhole wellbore. However, these differential pressure gauges have difficulty when that fluid is contaminated, leading to inaccurate measurements.
Heretofore, uses of absolute pressure sensors have been deployed in downhole conditions in order to compute differential pressure data however, until now, the computed accuracy and resolution resulting from the absolute pressure gauges do not provide the pressure differences of the order of a few percent of psi (i.e., 0.01 psi) required for accurate flow rate measurements, especially at lower flow rates. Absolute pressure sensors using known sensing technology, such as Quartz, Crystal Quartz Gauge, Sapphire, and the like, have failed to provide the transient response necessary for accurate flow rate measurements when fluid pressure drastically changes. Moreover, independently powered absolute pressure sensors based on an array of strain resistors comprising the elements of a Wheatstone bridge, have heretofore caused calculation errors or deviations within the output of these sensors due to divergent effects from having independent power supplies and/or circuitry.
As an example, U.S. Pat. No. 7,114,401 issued on Oct. 3, 2006 is directed towards a flow measurement system for steady-state and transient flow, particularly suitable for the drilling domain. The '401 reference, however, measures differential pressure by measuring the radial deformation, changes in the hoop strain/stress, of a sleeve upstream and downstream of a Venturi type section. On the contrary, the present disclosure is not directed to measuring deformation of the sleeve of a tool for obtaining differential pressure measurements.
It is therefore desirable to provide a method and apparatus for differential pressure measurement (e.g., which also can be referred to herein as a “system”) that takes advantage of the symmetry of at least two Wheatstone bridges in electrical connection, wherein the Wheatstone bridges are preferably selected, tested, and calibrated so as to minimize or cancel all common effects (i.e. temperature, power supply, drift, inelasticity, dynamic response, and the like), thereby addressing the above and other problems.